Conventionally, a scattered light-type smoke detection apparatus is used that detects smoke utilizing a light scattering phenomenon caused by smoke. The scattered light-type smoke detection apparatus includes: a smoke detection space into which smoke flows from the outside; a light-shielding structure for blocking light from the outside from entering the smoke detection space while allowing smoke from the outside to flow into the smoke detection space; a light emitter for emitting detection light toward the smoke detection space; and a light receiver for receiving detection light scattered by smoke flowing into the smoke detection space (referred to as scattered light) and converting the received scattered light to electric signal.
In such a scattered light-type smoke detection apparatus, as a member, including the light-shielding structure, for forming the smoke detection space, for example, a material such as a black resin for absorbing detection light from the light emitter is used, but it cannot significantly reduce reflection from the surface of the member. Due to this, conventionally, light emitted by the light emitter and passing through the smoke detection space may, for example, be reflected by a flat surface part, an end face, an edge part or the like of a light-shielding member included in the light-shielding structure, the reflected light (referred to as internally scattered light) entering the light receiver. In this case, the steady level of the detection output of the light receiver (referred to as zero point level) may be elevated to decrease the S/N ratio, thereby reducing reliability.
Thus, a scattered light-type smoke detection apparatus that is designed to reduce internally scattered light has also been proposed. For example, a scattered light-type smoke sensor has been proposed in which a light-shielding member is ingeniously shaped and arranged such that detection light from a light emitter is reflected by the surface of the light-shielding member, as much of the reflected detection light as possible being discharged to the outside of a smoke detection space (for example, see Patent Document 1). [Prior Art Document] [Patent Document]
[Patent Document 1] Japanese Patent Application Laid-Open No. H6-342497